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Showing papers in "Journal of Non-crystalline Solids in 1976"


Journal ArticleDOI
TL;DR: The mixed alkali effect in glass refers to the large, orders of magnitude, changes in many properties when a second alkali oxide is added as discussed by the authors, such as electrical conductivity and loss, alkali diffusion, internal friction, viscosity and chemical durability.
Abstract: The mixed alkali effect in glass refers to the large, orders of magnitude, changes in many properties when a second alkali oxide is added. Properties most affected are those associated with alkali ion movement such as electrical conductivity and loss, alkali diffusion, internal friction, viscosity and chemical durability. The compositional dependence of these properties is briefly reviewed and examples are given of the relevance of the mixed alkali effect to the manufacture of commercial glasses. Also reviewed are various theories for this scientifically interesting effect.

719 citations


Journal ArticleDOI
TL;DR: In this article, the basicity of an oxide glass can be measured experimentally from the frequency shifts in the ultra-violet (UV) (s-p) spectra of probe ions such as Pb2+ and can be expressed on the numerical scale of optical basicity Λ (ideally Λ lies between zero and unity).
Abstract: The basicity of an oxide glass can be measured experimentally from the frequency shifts in the ultra-violet (UV) (s-p) spectra of probe ions such as Pb2+ and can be expressed on the numerical scale of optical basicity Λ (ideally Λ lies between zero and unity). It is possible to relate Λ with (i) the constitution, and (ii) the electronegativity of the cations (e.g. Na+, Si4+, etc.) of the glass, and the relationship allows microscopic optical basicities λ to be assigned to individual oxides and oxy-groups in the glass. These microscopic optical basicities are used for interpreting various aspects of the physics and chemistry of glass including refractivity, network coordination number changes, chemical durability, the glass electrode, UV transparency and the host behaviour of glass towards metal ions generally. Changes in glass basicity in going from one alkali metal oxide to another are also discussed. Finally, the concept of optical basicity, both as an experimentally obtained quantity and as a number calculated from glass constitution and electronegativity, is discussed in relation to the traditional approach to acid-base behaviour in glass.

686 citations


Journal ArticleDOI
TL;DR: In this article, the field effect technique is applied to the experimental study of N (ϵ) in specimens of a-Si prepared by the glow discharge method and by vacuum evaporation.
Abstract: The electronic properties of amorphous solids are largely determined by the distribution of localized states N (ϵ) in the mobility gap. In this paper, the field effect technique is applied to the experimental study of N (ϵ) in specimens of a-Si prepared by the glow discharge method and by vacuum evaporation. The experimental approach and the analysis of the results are discussed in some detail. N (ϵ) curves, extending over an energy range of up to 0.5 eV have been obtained for a series of glow discharge specimens, deposited at substrate temperatures between 310 and 570 K. The results show structure in the gap states, a well-defined minimum almost in the centre of the mobility gap and a rapid rise in N (ϵ), 0.18 eV below ϵ c , which is identified with the onset of band tail states. The field effect data confirm that the predominant conduction mechanism at room temperature changes from hole hopping to transport in extended electron states, as the Fermi level is moved through the minimum in N (ϵ) The effects of annealing on the state distribution have been investigated, showing that N ( ϵ f ) can be reduced by one or two orders of magnitude. The nature of the gap states is discussed and the divacancy is suggested as a basic model for the electronic states involved.

331 citations


Journal ArticleDOI
TL;DR: In this article, the effect of the relaxation of two-state structural defects on the elastic properties of glasses at low temperatures is described and experimental data on the ultrasonic attenuation in vitreous silica and borosilicate glass in the temperature range between 0.3 and 4 K and at frequencies between 30 and about 500 MHz are presented and explained by this theory.
Abstract: A complete theoretical description of the effect of the relaxation of two-state structural defects on the elastic properties of glasses at low temperatures is given. New experimental data on the ultrasonic attenuation in vitreous silica and borosilicate glass in the temperature range between 0.3 and 4 K and at frequencies between 30 and about 500 MHz are presented and explained by this theory. We propose that over the entire temperature range from our lowest temperature of 0.3 to about 100 K the attenuation is due to the relaxation of defects with similar atomic structure.

217 citations


Journal ArticleDOI
TL;DR: In this paper, an anomalous behaviour of the density was observed on melts in the binary chalcogenide system SexTe1−x up to a temperature of 950°C.
Abstract: Density measurements have been performed on melts in the binary chalcogenide system SexTe1−x up to a temperature of 950°C. Anomalous behaviour of the density was observed. At higher temperatures the density increased on raising the temperature up to a maximum whose position shifts to lower temperatures with increasing concentration of tellurium. This anomalous density behaviour clearly shows an increase of the average coordination number of atoms in the melt. This increase of CN is caused by a change of the bonding system because of the tendency of Te to form pσ bondings. It was assumed that there exist two distinct structures in thermodynamical equilibrium at each temperature according to a law of mass action, for which cooperation effects have to be taken in account. At low temperatures Te atoms easily accept a loosely packed structure I with the aid of selenium. At high temperatures even Se atoms develop a more densely packed structure II with the aid of Te.

176 citations


Journal ArticleDOI
TL;DR: In this article, the authors used differential scanning calorimetry (DSC) to examine the thermally induced transformations of bulk and thin-film amorphous alloys within a large portion of the GeSe-Te system.
Abstract: We have used differential scanning calorimetry (DSC) to examine the thermally induced transformations of bulk and thin-film amorphous alloys within a large portion of the GeSeTe system. Most chalcogen-rich compositions showed a discontinuous increase of heat capacity when heated through the glass transition temperature T G . The Ge-rich compositions, which could only be prepared as sputtered amorphous films, were invariably characterized by an irreversible exothermic crystallization process on heating, beginning at the crystallization temperature T X . Values of T g and T X have been tabulated for all alloys investigated and the compositional dependence of T g has been examined in the light of recent models for viscous flow in glass-forming chalcogenide systems. In addition, a region of liquid immiscibility has been observed in the vicinity of Ge 20 Se 40 Te 40 in which a GeSe 2 -rich liquid phase segregates from a tellurium-rich liquid phase. The existence and limits of this immiscibility region have been rationalized on the basis of ionic perturbations to the covalent bonding. The segregation of a GeSe 2 -rich liquid increases the concentration of GeSe bonds which are the strongest and most ionic of the six angle-bond types which can occur in this system.

153 citations


Journal ArticleDOI
J. Wong1
TL;DR: In this paper, room temperature infrared transmission spectra in the range 4000-250 cm −1 of binary (P=O) 2 O 3 SiO 2 mixtures on heated silicon substrates at 300-400° C have been obtained across the whole composition range.
Abstract: Room temperature infrared transmission spectra in the range 4000-250 cm −1 of binary phosphosilicate glass (PSG) films deposited by reacting argon- or nitrogen-diluted PH 3 SiH 4 O 2 mixtures on heated silicon substrates at 300–400° C have been obtained across the whole composition range. In all the as-deposited binary films, an absorption at ≈1300 cm −1 characteristics of the P=O vibration was found to persist, together with a couple of broad absorptions in the regions 1200-900 cm −1 and 500 cm −1 . Using a differential infrared technique the broad feature in the higher frequency region has been resolved into two well-defined bands at ≈1100 and 970 cm −1 . A detailed analysis shows that the intensity variation of the differential band at ≈1100 cm −1 conforms well, at least to 50 mol% P 2 O 5 , to a simple structural model that yields an analytic distribution of POSi linkages as a function of composition by assuming chemical mixing in the vapor-deposited P 2 O 5 SiO 2 system. Furthermore, the system may be written as (P=O) 2 O 3 SiO 2 in order to emphasize the similarity of its coordination scheme with that of the B 2 O 3 SiO 2 system studied earlier. The nature of these CVD films has also been elucidated by thermal and water treatments.

107 citations


Journal ArticleDOI
TL;DR: In this paper, the kinetics of transformation behavior of roller-quenched amorphous Pd 83 Si 17 and Pd 80 Si 20 alloys after linear and isothermal heating was reported.
Abstract: The kinetics of transformation behavior of roller-quenched amorphous Pd 83 Si 17 and Pd 80 Si 20 alloys after linear and isothermal heating is reported. The transformation was examined with electron microscopy, electron diffraction and electrical resistivity measurement. The crystallization of amorphous alloys with 17 at% Si begins with metastable ordered fcc solid solution. The ordered fcc solution is transformed to a ordered metastable phase with, probably, orthorhombic structure. The crystallization of amorphous alloys with 20 at% Si begins by formation of spherulites with lamellar structure. Using electron diffraction we found that spherulites consist of two phases - orthorhombic Pd 3 Si silicide and Pd-rich silicide. From resistivity measurements, activation energies of 28.5 kcal/mol for Pd 83 Si 17 and 80 kcal/mol for Pd 80 Si 20 , respectively, were calculated.

104 citations


Journal ArticleDOI
TL;DR: In this paper, the authors extended the kinetic treatment of glass formation by the introduction of continuous cooling (CT) curves to estimate the cooling rates required to form glasses of various materials.
Abstract: The kinetic treatment of glass formation is extended by the introduction of continuous cooling (CT) curves to estimate the cooling rates required to form glasses of various materials. The CT curves may be constructed from isothermal time-temperature-transformation curves following the approach originally suggested by Grange and Kiefer. The modified analysis is used to evaluate the effects of nucleating heterogeneities on glass formation. It is found that for the concentrations of such heterogeneities found in most liquids, those characterized by contact angles greater than about 100° have a negligible effect on the cooling rate required to form glasses. Heterogeneities with smaller contact angles, can, however, have a significant effect on glass formation, with the critical cooling rate increasing with decreasing contact angle. The effects on glass formation of changes in the contact angle of nucleating heterogeneities are also compared with the effects of changes in the thermodynamic barrier to nucleation (in the crystal-liquid surface energy).

102 citations


Journal ArticleDOI
TL;DR: In this article, the photodissolution rate is proportional to the light intensity absorbed in the As2S3 at the Ag interface, but photoelectrons ejected from the Ag into the As 2S3 also contribute.
Abstract: A new technique, measurement of the electrical resistance change of the Ag layer, is developed to study the kinetics of photodissolution of Ag in amorphous As2S3. It is shown that the photodissolution rate is proportional to the light intensity absorbed in the As2S3 at the As2S3Ag interface, but photoelectrons ejected from the Ag into the As2S3 also contribute. The process is shown to be two-stage. Firstly a critical “radiation damage” dose must be accumulated in the As2S3. Secondly, the Ag atom is photon-assisted across the As2S3Ag interface activation barrier.

91 citations


Journal ArticleDOI
TL;DR: In this paper, the infrared reflectivity of three forms of silica, α-quartz, vitreous silica and neutron-irradiated vitrerous silica (≈ 2.7 × 1020 neutrons cm−2) has been measured from 400-2000 cm−1.
Abstract: The infrared reflectivity of three forms of silica, α-quartz, vitreous silica and neutron-irradiated vitreous silica (≈ 2.7 × 1020 neutrons cm−2) has beenmeasured from 400–2000 cm−1. These data have been analysed by a Kramers-Kronig transform to give the real and imaginary parts of the complex dielectric constant. Considerable care has been taken to identify and minimize errors arising in the measurements of the reflectivity spectra and in the subsequent analysis. Data are presented for the optical constants, oscillator frequencies, band strengths and halfwidths of each band. The spectra for vitreous silica and neutron-irradiated silica show two regions of absorption which are not present in the crystalline form — a strong band is observed near 950 cm−1 and a broad band from 600–800 cm−1. A difference spectrum obtained by subtracting the spectrum of the imaginary part of the dielectric contrast for vitreous silica from the corresponding data for neutron-irradiated silica reveals more detailed structure in the form of a weak but sharp band at 620 cm−1. Interpretation of these results is contained in a companion paper.

Journal ArticleDOI
TL;DR: In this article, the structure and semiconducting properties of amorphous vanadium pentoxide obtained by splat cooling have been studied and it has been shown that the electronic mobility is lower in the vanadium state than in the orthorhombic V 2 O 5.
Abstract: Structure and semiconducting properties of amorphous vanadium pentoxide obtained by splat cooling have been studied. Long-range order appears suddenly when the oxide is heated to about 200°C. The short-range order of the glass seems to be almost identical to that encountered in orthorhombic V 2 O 5 . ESR spectra are typical of localized electrons, they show that the electronic mobility is lower in the amorphous state. The hopping frequency of the unpaired 3d electron from a V 4+ to a V 5+ ion increases when long-range order is established. This phenomenon is related to the electrical resistivity which is about one order of magnitude higher in the glass.

Journal ArticleDOI
TL;DR: In this paper, a method for pinning the Fermi level of insulators to that of a metal calibrant is described, resulting in the ability to obtain absolute binding energies of the electronic levels in wide bandgap insulators.
Abstract: Fourier deconvolved X-ray photoelectron spectroscopy (XPS) valence band spectra obtained from crystalline and amorphous silica, used in conjuction with the results of quantum chemical calculations of the SiO4 tetrahedral unit and other spectrometric measurements (soft X-ray emission, UV absorption and reflectivity, photoconductivity, photoinjection and energy loss spectroscopy), suggest a reinterpretation of the electronic band structure of silica that is consistent with all the data. A unique method for pinning the Fermi level of insulators to that of a metal calibrant is described, resulting in the ability to obtain absolute binding energies of the electronic levels in wide bandgap insulators. Observe peaks in UV reflectivity and energy loss spectra of silica are all assigned to direct interband transitions, and no excitonic states need be involved to explain the data. Upper and lower limits for the bandgap of dry crystalline (α-quartz) and amorphous (Corning Code 7940 glass) silica are adjusted downward from the 8.9 eV bandgap proposed by DiStefano and Eastman [1] to 7.8–5.55 eV for α-quartz and 7.3–5.05 eV for fused silica, respectively. This in no way compromises the obvious insulating properties of silica in MOS devices, since the conductivity is governed by the high barrier height (∼3.8 eV in the case of gold) for metal-insulator electron transfer. The lowered bandgap results from increased low-energy electron density in the valence band, which we ascribe to the 1t1 molecular orbital predicted by various quantum formalisms, but heretofore not detected experimentally in bulk (thick) silica. Disappearances of this orbital and rearrangement of the non-binding 5t2 and 1e orbitals in silicas rich in silanols (OH), as may be the case for thin-film silica on Si metals, would increase the bandgap to 8.3 eV, in better agreement with previous determinations.

Journal ArticleDOI
TL;DR: In this paper, the reaction rate of removing ions from a zircono-silicate glass fibre by aqueous extracts of Portland cement has been experimentally determined, and the significance of these results in the interpretation of the durability of ZS-glass fiber cement composites is discussed.
Abstract: The rate of removal of ions from a zircono-silicate glass fibre by aqueous extracts of Portland cement has been experimentally determined. To accelerate the reaction, digestions have been carried out at elevated temperatures. The reaction rate for the glass composition investigated favours a log-time dependence. The reacted fibres show a relative enrichment of Zr on the surface, although no definite zirconia-containing phase has been identified. Soda-lime and borosilicate glass fibres which have been similarly examined for comparison purposes, required considerably shorter periods of digestion to produce suitable concentrations of glass breakdown products. The reaction rate for soda-lime glass appears to be largely controlled by Na+ diffusion. With borosilicate glass, no simple interpretation can be applied to the breakdown mechanism because of the complex nature of the reaction products. The significance of these results in the interpretation of the durability of zircono-silicate glass fibre cement composites is discussed.

Journal ArticleDOI
TL;DR: In this paper, a model liquid consisting of 336 atoms arranged in a computational cell with periodic boundaries and with the atomic intereaction represented by the Lennard-Jones pair potential was used to study the thermodynamic and structural properties of non-crystalline solid structures.
Abstract: The molecular dynamics technique was used to study the thermodynamic and structural properties of non-crystalline solid structures. The structures were obtained by quenching a model liquid consisting of 336 atoms arranged in a computational cell with periodic boundaries and with the atomic intereaction represented by the Lennard-Jones pair potential. The characteristics of the resulting non-crystalline atomic configurations were found to depend weakly on the applied quenching rate.


Journal ArticleDOI
TL;DR: In this article, the authors examined optical constant data for vitreous silica and neutron-irradiated (NIR)-vibrational spectra of glasses, given in part I are examined in an attempt to gain further knowledge of the structure of the glass strong features of the spectrum can be described by band broadening parameters.
Abstract: Optical constant data for vitreous silica and neutron-irradiated vitreous silica, given in part I are examined in an attempt to gain further knowledge of the structure of the glass Strong features of the spectrum can be described by band broadening parameters, which are calculated using an extension of the Wilson GF matrix method, and are shown to be quantitatively related to the distribution of SiO distances and oxygen bond angles obtained from X-ray scattering data The approximation commonly used to generate the optically active vibrational spectra of glasses, namely to form the product of the vibrational density of states function and a weakly frequency-dependent intensity factor gives a relatively poor representation of the experimental spectrum The magnitude of ‘disorder-induced’ absorption in regions well away from the major bands is semi-quantitatively estimated by subtracting the contributions of the major bands Interpretation of some of the features of this difference spectrum is possible in terms of vibrations of non-bridging oxygen atoms, but if this interpretation is correct, it is necessary to postulate clustering of ‘dangling’ oxygen atoms, which would not be consistent with a random network model for the structure An alternative explanation, that the vibrations are framework modes, leads to the conclusion that the preferred configuration in vitreous silica resembles the arrangement of silicon-oxygen tetrahedra in cristobalite

Journal ArticleDOI
TL;DR: In this paper, a reversible optical transition has been found in thin films of SeGe and PSeGe glasses. But the authors did not consider the presence of arsenic in these glasses.
Abstract: A reversible optical transition has been found in thin films of SeGe and PSeGe glasses. This optical transition is similar to that found in AsSeGe and AsSeSGe glass films; heating causes the shift of the absorption edge to shorter wavelengths, and illumination moves it to longer wavelengths without crystallization. It was found that the presence of arsenic is not always necessary. Fundamental optical properties of these glasses, i.e. absorption constant, optical energy gap, change of the optical energy gap, and the refractive index by heating and illumination are reported. Change of the optical energy gap and the refractive index is small in SeGe and PSeGe glasses, compared with that in AsSeGe and AsSeSGe glasses.

Journal ArticleDOI
TL;DR: In this article, the authors measured the transport number of Ag ions in the glass-forming region in the system P 2 S 5 Ag 2 S glasses and found that the transport numbers of Ag ion sites in the nonconducting framework composed of both S anions and As, Ge or P cations.
Abstract: The glass-forming region in the system PSAg was determined and density, thermal expansion, dc conductivity and the transport number of Ag ions were measured for P 2 S 5 Ag 2 S glasses found in the PSAg system. The results for the transport number measurement show that P 2 S 5 Ag 2 S glasses are purely ionic conductors owing to the Ag ion migration, like most of the As 2 S 3 Ag 2 S and GeS 2 GeSAg 2 S glasses reported previously. Glass structure and ionic conduction processes in As 2 S 3 Ag 2 S, GeS 2 GeSAg 2 S and P 2 S 5 Ag 2 S glasses are discussed, based on their ionic conductivity and density data. The structural concept of α-Ag 2 S was applied to these glasses, which suggests that the Ag ions in the glasses are distributed in the available Ag ion sites in the non-conducting framework composed of both S anions and As, Ge or P cations. In each system the ionic conductivity increases linearly with increasing Ag + /total cation (%) in glass composition, the determining factor being the activation energy for ionic conduction alone. Thus, the activation energy in these glasses depends predominantly upon the molar ratio of Ag ions to total cation in the glass, irrespective of the kind of system. Small differences in the activation energy among the three systems can be interpreted as arising from differences in the field strength of As, Ge and P cations.

Journal ArticleDOI
TL;DR: In this paper, the authors show that the resistance of chalcogenide memory devices switched with pulses which have a long or very short trailing edge, showed no significant difference.
Abstract: Measurements of the resistance of chalcogenide memory devices switched with pulses which have a long or very short trailing edge, showed no significant difference. This contradicts the switching model as proposed by Cohen et al. Experimental data is presented and a discussion of the complexity of crystallization suggests a modification in which the inner zone of the filament is usually quenched below the crystallization temperature during the set pulse, as a result of current redistribution. Further modifications to the model for the reset event take account of an annulus around the reset filament which is at the optimum temperature for crystallization. Crystallization in that annulus results in shifting of the filament axis. The use of multiple-pulse resetting reduces the chance of crystal growth in the annulus.

Journal ArticleDOI
TL;DR: In this paper, density measurements were performed on melts of the binary chalcogenide system GexSe1−x (0.5) up to 1000°C and the anomalous density behaviour of the melts clearly showed a change of short-range order from a less to a more densely packed structure, caused by the development of a pσ-bonding system.
Abstract: Density measurements were performed on melts of the binary chalcogenide system GexSe1−x (0 ⩽ x ⩽ 0.5) up to 1000°C. The isotherm of molar volumes Vm at 750°C shows a relative maximum near GeSe2. Molar volumes of the system behave linearly between GeSe and Se at 1000°C. Vm's of melts between x = 0.30 and x = 0.35 decrease at high temperatures on heating. The anomalous density behaviour of the melts clearly shows a change of short-range order from a less to a more densely packed structure, caused by the development of a pσ-bonding system. Within the composition range 0 ⩽ x ⩽ 1 3 the short-range order at lower temperatures is determined mainly by GeSe 4 2 tetrahedra linked directly corner-to-corner or via Se atoms. At higher temperatures pσ bonds arise more and more, even in melts rich in selenium. Within the composition range 1 3 ⩽ x ⩽ 0.5 the short-range order is mainly determined by a distorted octahedral configuration, even at lower temperatures. From the short-range orders of melts and from crystalline structures of GeSe2 and GeSe, the tendency of glass formation from the melt is discussed in detail.

Journal ArticleDOI
TL;DR: In this article, the authors present measured data on glass transition temperature, thermal expansion, density, hardness, refractive index and electron microscopy of GeAs-As-Se glasses and bring together some literature data on viscosity and mechanical properties.
Abstract: This paper presents measured data on glass transition temperature, thermal expansion, density, hardness, refractive index and electron microscopy of GeAsSe glasses and bring together some literature data on viscosity and mechanical properties Interpretation of this information to identify suitable compositions for bulk synthesis is discussed

Journal ArticleDOI
TL;DR: In this paper, the internal friction and shear modulus of amorphous Pd 80,Si 20, Fe 80,P 13,C 7 and Fe 50,Ni 33,P 12,C 5 alloys have been measured at about 05 Hz over a temperature range from room temperature to about 550°C.
Abstract: The internal friction and the shear modulus of the amorphous Pd 80 –Si 20 –, Fe 80 –P 13 –C 7 and Fe 50 –Ni 33 –P 12 –C 5 alloys have been measured at about 05 Hz over a temperature range from room temperature to about 550°C The internal friction rises steeply with temperature and shows maxima around the crystallization temperature The activation energy for the steeply rising internal friction has been estimated by the two different procedures; from the shift of the curve by the frequency change and from the slope of the In Q −1 versus 1/ T plot The two values are very different, which indicates the existence of a wide distribution of activation energies Crystallization of the amorphous alloys resulted in an increase of about 30% in the shear modulus

Journal ArticleDOI
TL;DR: The Mossbauer spectrum of amorphous iron-phosphorus has been measured for alloys having compositions ranging from 15 to 25.8 at% phosphorus as discussed by the authors, which indicated a large number of different iron sites having the same compositional short-range order as the crystal.
Abstract: The Mossbauer spectrum of amorphous iron-phosphorus has been measured for alloys having compositions ranging from 15 to 25.8 at% phosphorus. Measurements were made at ambient temperature and also above the Curie temperature. The Curie temperature was measured by an induction method and increased linearly from 280 to 300°C with decreasing phosphorus content. The results indicated a large number of different iron sites having the same compositional short-range order as the crystal.

Journal ArticleDOI
TL;DR: Germanium thin films were prepared in an amorphous form by vacuum deposition onto room temperature fused silica substrates in this article, where the optical transmission near 0.65 μm was measured, where the absorption constant is most sensitive to phase transformation.
Abstract: Germanium thin films were prepared in an amorphous form by vacuum deposition onto room temperature fused silica substrates. The amorphous—crystalline transition was studied as a function of time and temperature by measuring the optical transmission near 0.65 μm, where the absorption constant is most sensitive to the phase transformation. At a fixed temperature, the time for half the volume of the sample to become crystallized was found to be consistent with the relation tc = τ exp(E0/kT), with an activation energy E0 = 2.96 eV.

Journal ArticleDOI
TL;DR: Based on a series of experimental results, a model for photodoping was proposed in this paper, and the square root dependence for the growth of the photodoped depth with exposure time was explained in the light of this proposed model.
Abstract: The photo-enhanced reaction between metallic silver and vitreous chalcogenides is known as “photodoping”. Based on a series of experimental results, a model for photodoping was proposed. It was assumed in this model, that a junction barrier at the silver-chalcogenide interface worked for separating photocarriers. Holes are captured by metallic silver, and electrons are trapped by active or loosely bound chalcogen atoms after travel toward the interior of a glass layer. The Coulomb attraction field between ions thus formed is large enough to overcome the kinetic barrier in the process of silver diffusion. The square root dependence for the growth of the photodoped depth with exposure time has been explained in the light of this proposed model.

Journal ArticleDOI
TL;DR: In this article, the authors measured the thermodynamic properties of both melt-quenched and evaporated selenium and found that the relaxation peak occurred between 320 and 330 K, and had an activation energy of ≈22.5 kcal/mole.
Abstract: Thermal relaxation phenomena were measured in samples of both melt-quenched and evaporated selenium. On the basis of earlier studies, the two methods of preparation produced samples with polymeric chain concentrations of 30–50% and 0% respectively; the rest of the material was in the form of eight member rings. The relaxation peak occurred between 320 and 330 K, and had an activation energy of ≈22.5 kcal/mole for the melt-quenched sample. A decrease of 1 K in the glass relaxation temperature and 0.5 kcal (a at) −1 in the activation energy was observed in samples which had been initially evaporated. No change was observed as a result of melting and quenching these evaporated samples. It is postulated that there was no change when the evaporated sample was melt-quenched be because rings and chains can interconvert and equilibrate relatively readily at temperatures as low as T g (50° C), and consequently the samples all had the same structure after once being heated above T g . The differences observed are probably due to accidental impurities in the evaporated samples which help catalyze the interconversion of rings and chains. Further, since the equilibrium concentration of polymeric chains is temperature dependent, it is postulated that the large relaxation effects seen at T T g are due to the equilibration of these chains with the rings. The observed activation energy for the relaxation supports this view. It is about the same energy as has been previously measured for Se 8 ring breaking in liquid selenium. Two consequences of this postulate are that the selenium analog to the sulfur polymerization transition must occur well below room temperature if it exists, and therefore, that the equilibrium ring-chain ratio can be smoothly extrapolated down to room temperature from the published high-temperature data.

Journal ArticleDOI
TL;DR: In this paper, the fraction of four-coordinated BO4 units has been determined via computer analysis of the NMR spectra; the method is similar to that employed previously for binary and other ternary borate glasses.
Abstract: 11B and 27Al nuclear magnetic resonances (NMR) in glasses of the NABAL system Na2OB2O3Al2O3 have been studied as a function of composition. From the boron data, the fraction of four-coordinated BO4 units has been determined via computer analysis of the NMR spectra; the method is similar to that employed previously for binary and other ternary borate glasses. The 27Al NMR indicates no abrupt change in the average aluminum environment. Certain linear relationships have been found which yield detailed information on the competing processes of BO3, BO4 and AlO4 formation, and the formation of triclusters consisting of three tetrahedra having one oxygen in common. Furthermore, it is concluded that the oxygen available for the formation of various aluminum-containing species is a function of the soda concentration only and that the conversion to AlO4 is favored as compared with BO4.

Journal ArticleDOI
TL;DR: In this paper, the transformation range viscosity, activation energy for viscous flow and the dilatometric critical temperature of sodium trisilicate glasses are all decreased by addition of water, whereas the thermal expansion coefficient in the elastic region is not altered to a significant extent.
Abstract: The transformation range viscosity, activation energy for viscous flow and the dilatometric critical temperature of sodium trisilicate glasses are all decreased by addition of water, whereas the thermal expansion coefficient in the elastic region is not altered to a significant extent. Although these effects are similar to those observed in vitreous silica, they are considerably reduced in magnitude. Since sodium trisilicate glasses are already highly depolymerized by the presence of Na 2 O, the additional depolymerization due to small additions of water does not seem adequate to explain these results. It is suggested that water behaves similarly to the alkali oxides and that the results of this study may be due to an extreme case of the mixed-alkali effect.